I'll put a different spin on this. I don't have a keezer but I lager in a freezer so it's pretty much the same thing. My temp controller is an arduino so I've coded how it cycles. I set a target air temp, and a heating/cooling mode. Obviously it's in cooling mode for this. Heating if for my HLT. When the temp is above the target, it turns the freezer on for 30 seconds, once it's run for 30 seconds, it checks the temp every 10 seconds until the target temp is passed. Seeing as it's a 3cu.ft freezer, 30 seconds is usually enough to get the fluid running through the freezer and drop the temp below the target. A 30 second run usually drops the freezer air about 5 degrees, 4 of which happen after the compressor has already shut off. Pretty sure it cycles about once every hour and a half or so. I've never really timed it. As long as it's not cycling so fast that it's causing damage to the compressor I've never really cared.
Edit: Geez nevermind. That cycle was 15 minutes. I think the deal is the probe is too close to the inside wall of the freezer. Hah, it's probably holding the average temp to a degree or two. Oops.
Edit Again: No it needs a differential. Don't turn on until you're a (differential amount) past the target, don't turn off till you've passed the target. Unless the freezer is big it will always drop the temp enough by 30 seconds to shut down the compressor.